There are known various types of vibration isolation devices, which are so designed as to absorb vibration generated from a vibratory source such as an engine, thereby suppressing transmission of the vibration to a support body on which the vibrator source is mounted. One example of such known vibration isolation devices takes the form of a liquid-filled vibration isolation device, which comprises a first attachment member adapted to be attached to an engine as a vibratory source, a second attachment member of tubular shape adapted to be attached to a support body, an elastic member such as rubber interconnecting the first and second attachment members, and a diaphragm mounted to the second attachment member so as to define, together with the elastic member, a liquid chamber. A partition member is mounted to separate the liquid chamber into a main compartment and an auxiliary compartment that communicate with each other via an orifice. By virtue of the effect of a restricted flow produced when a working fluid passes through the orifice between the main compartment and the auxiliary compartment, vibration generated from the engine can effectively suppressed before being transmitted to the support body.
In recent years there has been an increasing demand for a lightweight and inexpensive vibration isolation device. To meet this requirement, a main concern has been addressed to employ a plastic bracket for attachment of the second attachment member to the support body, such as disclosed in Japanese Patent Laid-Open Publications (JP-A) Nos. 8-247208, 9-177866 and 2001-50331.
A vibration isolation device shown in JP 8-247208 A includes a tubular bracket formed from a synthetic resin and connected at one end with an elastic member. A partition member, a diaphragm and a metal cap are fitted in the named order into the tubular bracket from an end opposite to the elastic member. The metal cap is directly press-fitted with the plastic bracket.
In a vibration isolation device shown in JP 9-177866 A, a tubular bracket formed from a synthetic resin is connected to an elastic member and includes a tubular metal bracket member integrally molded as an insert with the plastic bracket when the plastic bracket is formed by injection molding. The metal bracket member is disposed internally of the plastic bracket along substantially the entire axial length of the plastic bracket. A partition member, a diaphragm and a dish-like metal cap are fitted in the named order in the tubular metal bracket from a side opposite to the elastic member, and then an outer end of the metal bracket member is bent in a radial inward direction to clench or hold the partition member, diaphragm and the metal cap. A vibration isolation device shown in JP 2001-50331 A has a similar configuration.
In the vibration isolation device shown JP 8-247208 A, the plastic bracket as it is press-fitted with the metal cap is subjected to an external force acting in a radial outward direction thereof. If such external force is insufficient or excessively small, reliable press-fit engagement between the plastic bracket and the metal cap cannot be achieved. Alternatively, if the external force is excessively large, the plastic bracket may be damaged or broken. To avoid this problem, the plastic bracket and the metal cap both require severe dimensional and quality control, which will incur additional cost and man-hours.
Furthermore, in the vibration isolation devices shown in the above-named three Japanese publications, the partition member, diaphragm and metal cap are assembled in succession into the bracket so as to form a liquid seal assembly. In general the elastic member and the liquid seal assembly vary in specifications depending on the type of a vibratory source with which the vibration isolation device is used, whereas the bracket is used commonly with different types of vibratory sources. It is therefore preferable that a group of elastic members of different specifications and a group of liquid seal assemblies of different specifications are prepared in advance as subassemblies. In an actual application to a particular vibratory source, a suitable one of the elastic members and a suitable one of the liquid seal assemblies each stocked in the form of a subassembly are selected and assembled with a tubular bracket. This arrangement is in fact effective to increase the assembling efficiency and lower the man-hours.
When used in combination with a plastic tubular bracket, the elastic member or the liquid seal assembly that is prepared in the form of a subassembly is preferably assembled by press-fitting operation with the plastic tubular bracket because the press-fitting operation is highly efficient. To ensure reliable engagement between the plastic bracket and the elastic member or the liquid seal assembly, the press-fitting operation requires severe dimensional and quality control of the two parts to be press-fitted, which will incur an increase in the cost and man-hours.